63 Ampeg super echo twin 2?

[Toxophilite]

So far this is an easily reversible comparatively simple modification.
It works well being much more versatile though obviously there is a lot more insertion loss.


The knobs on my dual concentric pot are a little high (cobbled together as I didn't have the originals and the pots posts had to be cut down a good 3/8") but I have other choices and I can modify it a bit more to make it lower profile


In this incarnation I put the tone stack before the volume pot in the signal path


I have 2 questions:


1-Does it matter which comes first?
The volume pot chicken or the tone pot egg?


Though the amp still seems very loud I've of course lost a fair amount of gain by scooping the mids (I like this control with the treble and bass almost at max)
For live I would probably use the accordion input(higher gain) for sure


2- Are there any relatively simple and not too invasive mods I could do to up the gain a little without changing the amps character too much?
It doesn't need to get a drastic amount louder but a little might be good.

[SILVERGUN]

You could try disconnecting the NFB on one or both channels.

[Toxophilite]

I think there might be not too much negative feedback being used in this amp as is, but I certainly could mess with taht
Some new 7591s might help too


I have a question about the James tone stack
I basically used this one but with 1M pots and I have a 250pf on the top of the treble pot instead of the 330pf


ON the one on my tone stack calculator there's a 1 meg resistor going to ground on the output
What difference does that make and why is it there?
(i just heard S.Luckey typing in my head saying "Clip one in and find out!")


if anyone has insights on my questions from my previous post too it would be much appreciated.

[SILVERGUN]

answer to question #1 from earlier post - no, it doesn't matter

[sluckey]

ON the one on my tone stack calculator there's a 1 meg resistor going to ground on the output
What difference does that make and why is it there?

I think that's just to represent a load resistance. Most of the model circuits in that tsc show a load resistor on the output.

[shooter]

Are there any relatively simple and not too invasive mods

the PA is cathode biased, do the math and see if you can tweak on the 140 R, bigger bypass cap?
change over to JJ6V6 and run 'em glowing

[Toxophilite]

Oh heck now I have to look up how to do the math!

[Toxophilite]

I'm not getting any noise out of the main filter caps so at this point I'm replacing all the little guys.
I'm not getting big voltages readings on the grids
Is it worth it to replace the coupling caps, there's not tonnes of them, about 4 a side


The ones on the output tubes are .02 would it hurt to bump up to .033 or .047 to get more bottom coming though the amp?


Interestingly the cathode bias cap for the power tubes is 20mfd/50V on the schematic. Each actual amp is using a  25mfd/25V section of the Can cap.


I know have a 22K resistor on the feedback loop instead of the original 10
Definitely louder and not significantly noisier


I also tried a bright cap on my volume control on the side that now has the James stack. It makes a barely discernible effect, not at all like the dramatic effect (and rise in hiss) that the bright cap makes in a fender amp.


Are there factors which make this a darker sounding amp? (besides the tone stack)

oh and I have one plate voltage that's kind of high pin 2 of V6 (V6A on schematic) the preamp tube(1st gain stage) on the left channel looking at the schematic. I say this because the Piazzo redraw and the original schematic label each channel differently. It should be 170v and it reads 211v .
The dropping resistor on the plate reads okay (around 120k)  and the voltage before that and on the PI prior all read pretty well spot on.
It shares a cathode bypass cap and resistor with the right side preamp tube.
It reads 2.1 volts (the schematic says 2.4) the other preamp tube has a normal plate voltage I think 173V


I tried a different tube, same readings so I'm beginning to think it's .o5 couple cap to the tone stack and then PI
On the tone stack side of the cap I get a 10V reading


I'm going to try swapping it out

[sluckey]

I'm not getting big voltages readings on the grids

All tubes in that amp should have zero volts on the grids. If you have anything greater than 0.1v you should do a leakage test on the coupling caps.

It should be 170v and it reads 211v .

I would not worry about that. I think the 170v listed on the schematic is wrong. This tube has a 120K plate resistor and the corresponding tube in the other channel has a 270K plate load resistor. It also shows 170V. One of those voltages has to be wrong and the one with the smaller plate load will have a smaller voltage drop across the plate load, meaning the plate voltage will be higher.

I'm beginning to think it's .o5 couple cap to the tone stack and then PI
On the tone stack side of the cap I get a 10V reading

The voltage on the tonestack side of that cap should be zero. Time to do the leakage test on that cap.

[Toxophilite]

Thanks!


I already shotgunned that one and put a new sprague in. The old one had been causing my volume pot to be VERY noisy when turned, now it's dead quiet, voltage on that plate reads 204 now.
I will try the test on the same cap on the other channel as it was showing a small voltage on the grid side


The original schematic is funny, it's a little hard to tell who's who
For example the channel on the schematics left side is labelled Channel 2, however it would seem to be the channlel with the bias vary trem. Also it is the one driving the reverb tank  which comes back in channel 2


On the faceplate, Channel one is definitely the one with the bias vary trem and the reverb shows up in channel two!!
Pretty damn confusing!

[Toxophilite]

Out of curiousity
The resistors on the inputs (and grid of the 1st gain stage 6SL7)  are 120k, I'm of course using to seeing the fender values of 68k or 34k when they're in parallel.
is the 120k necessary for the 6SL7 ?


Could I go lower and would I get a bit more volume out of the 1st gain stage if I did?


Also the whole guitar accordion input thing confuses me. it seems like it's probably some sort of parallel resistor deal like fender inputs. Somehow the jacks with switches confuses me on this schematic.


Does the guitar input have 120k and the accordion 60K (2  120 in parallel) ?


Oops answered this question with my DMM..duh!

I tried 2 68K, much louder as well as a couple of 100K. Any issues with going to the 68K in this circuit?


Thanks

[sluckey]

Any issues with going to the 68K in this circuit?

No issues.

[Toxophilite]

Thanks
So I was playing the amp at volume(Dimed in the 'hot' input) with a James tone stack in channel one, a 22k NFB resistor (original was 10k) and 68k resistors on the inputs(originall120k)
THe James stack obviously yanks most of the volume(in the form of mids) out of the amp and the other changes were meant to help counter that.

It sounds great, however my 40 watt 2x 10 vibrolux reverb build  in a 20" by 19" cab can easily match it and more and it only weighs about 39lbs

And frankly my changes have all been to make the amp sound more scooped and perhaps fenderish.
The two 12's sound nice and it would likely be a lot louder with some uber efficient ones..like eminiences little texas 4 lbs neo speakers.
and to make it a decent weight (it's currently 52 lbs) for it's wattage, it would best to put it in a slightly smaller lighter cab

It seems like a lot of expense and work to do to make something expensive into something it isn't!!

I could build my own version of this concept for a fraction of the price(recycled parts etc) and likely about about 45lbs max
put this one back to original but with new caps and sell it to someone who wants this sound and this amp in particular.

However it has been lot's of fun playing with it, learning and getting cool ideas for my own stereo amp build.

[Toxophilite]

Steve had asked about gut shots so I took some

[Toxophilite]

last photo

[sluckey]

THX